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| Tarts can be an example of phase transition as the fillings change from liquid to solid forms. |
The boss at Chez John declared my previous post on Energy, Temperature and Heat a review that crossed his eyes. He's got a point; a lot of this food science is food for thought, and some of it's bitter to swallow. Then along comes an aha! moment and you feel better. Here was one of my first in the Harvard course.
Aha! Moment With Alcohol: Why do we add vanilla or liqueur after a recipe has been heated and begins to cool? We say well, the alcohol would evaporate, but do you know why it does? Turns out that ethanol (pure alcohol) is liquid at room temp, and this is why we can pour ourselves a gin martini while thinking about the problem. However at 78 Celsius (about 172.4 degrees fahrenheit), it becomes a gas. That's why it might evaporate if your liquid is too hot. And that's the lead-in to phase transitions. Ethanol changes from a liquid to a gas. Voila!
Phase transitions happen when a substance changes from one state to another (solid, liquid or gas).
To get into this further, enter Chef Joan Roca, who some say is the No.1 chef in the world. Mon dieu!
Joan Roca shows you how to transform eggs, sole filet and anemones all through sous-vide cooking. Yep, some of the Harvard lectures are in languages other than English, but each includes a transcript so you can watch and read along.
Tool that's new to me: The rotovap (rotary evaporator). It's used to concentrate flavors in foods, freeze-dry foods at very low temperatures and separate dangerous, volatile compounds like methanol from cocktails. It does this by creating a vacuum, and that lowers the pressure around the food. (So the opposite of the rotovap is a pressure cooker.)
No. 3 Equation of the Week: U interaction = C x kbT
This formula represents the physical balance between the fact that molecules like to stick together (stay solid) and also like to jiggle around and evaporate off. There are many ways to change phases of food from solid and liquid to gas. You know one of them - temperature - but another is pressure (which happens by raising pressure in a pressure cooker, or lowering it in a rotovap. See, you just learned this if you made it this far).
Cool lab experiment: Yes, you can make a small amount of ice cream in a baggie, just following directions and using your hands - no ice cream crank at all. It's a demo of how a liquid turns into a solid - and that's a phase transition!
Number of Pages of Notes: 21
(am I improving on note-taking?)
Next up: Elasticity in Week 4, and if you think it's all about stretchy dough, not so fast.
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